上升流中微生物对氨氧化速率影响的研究

Biogeochemical cycles induced by the coastal upwelling is a hot research topic. The coastal upwelling drives water with low temperature, high salinity and nutrients to the surface, and contributes greatly to the surface fertilization, primary production and nitrogen cycles. Ammonia oxidation to nitrite as the first rate-limiting step of nitrification plays a major role in marine nitrogen biogeochemical cycles. However, by far the microorganism-mediate ammonia-oxidization process has not been well studied, especially, the impacts of those microorganisms on the ammonia oxidization rates were largely unknown. Coastal upwelling off the East HaiNan Island is a typical one in China, and it occurred due to the intensification of the south-west monsoon during summer. In this study, molecular tools, such as metatranscriptomics and real-time quantitative PCR on the amoA gene, will be applied to investigate the community structure and abundance of active ammonia-oxidizing archaea (AOA) and bacteria (AOB) along the depth profiles in both upwelling and non-upwelling regions. Ammonia oxidization rates will be measured by 15N-tracer experiment as well. The data obtained will help to elucidate the variation of AOA and AOB induced by the coastal upwelling and their relationships with the ammonia oxidization rates in different water depths and to estimate the contribution of ammonia-oxidization to the total primary production and the ultimate marine nitrogen cycles in the coastal upwelling systems.

沿岸上升流中微生物介导的地球化学循环过程是国际前沿研究领域。通过上升流可将底层低温、低氧、高盐、高营养盐的海水带到上层，大大促进了上层海水中的初级生产力和氮循环过程。氨氧化作为硝化反应的第一步限速反应，在氮循环中有重要作用。但目前国内外对于上升流中微生物介导的氨氧化过程研究还很少，特别是与氨氧化速率的相关性研究还基本是空白。琼东上升流是我国典型的沿岸上升流，受西南季风影响于夏季4-9月形成。本项目拟以琼东上升流和非上升流海域不同水层中的氨氧化细菌和古菌作为研究对象，采用环境转录组学和荧光定量PCR技术，来研究具活性的两大类功能组群的结构组成和丰度。同时采用同位素示踪法测定不同水层中的氨氧化速率。通过本项目可以探讨上升流中微生物对氨氧化速率的影响，评估上升流区微生物介导的氨氧化过程对初级生产力及氮循环的贡献。

沿岸上升流可将深层低温、低氧、高盐、高营养盐的海水带到上层，进而促进上层海水中的初级生产力和氮循环过程。氨氧化作为硝化反应的第一步限速反应，主要由微生物所介导，是氮循环的关键步骤。但目前国内外对于沿岸上升流中微生物介导的氨氧化过程研究还很少，特别是与氨氧化速率的相关性研究还基本是空白。本项目以琼东上升流为示范区，以上升流和非上升流海域的表层（5米）和底层（25米）的氨氧化微生物作为研究对象，应用高通量测序、荧光定量PCR、15N同位素标记示踪法等技术开展了氨氧化微生物的分子生态学研究并测定了不同水层中的氨氧化速率。项目取得的主要研究成果如下：（1）阐明了琼东上升流区域中的氨氧化微生物以氨氧化古菌(AOA）为绝对优势种，氨氧化细菌基本检测不到；（2）揭示了琼东上升流可显著提高AOA的丰度，但对其群落结构无明显影响；（3）摸清了影响氨氧化古菌群落多样性和丰度的主要驱动因子，两者与海水盐度、硅酸盐含量呈显著正相关，而与温度呈显著负相关；（4）评估了琼东上升流海域的氨氧化速率，揭示了氨氧化古菌与氨氧化速率的相关性。这些研究结果促进了对氨氧化微生物对沿岸上升流响应的进一步认识，为深入了解微生物参与海洋氮循环过程提供了重要参考。